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Tire pressure odyssey, what am I doing wrong? (self.bikewrench)

submitted 8 months ago by Natal to c/bikewrench

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Hello everyone.

I recently got myself a mountain bike from Canyon. It all works, got myself all the gear, pumps and all. And the pressure gage give me a reading of 10 PSI, which is odd because the tires are firm. 10 PSI should be nearly flat.

I have other pumps, including one that works for my car too, which I trust because I cross checked its values with my mechanic.

Here's the odd thing. I got the bike out and plugged it to the car tire pressure device and it also gave me a reading of 10 PSI. I also have a Topeak Shuttle Gage, 10 PSI.

How is that possible? I can't really believe all three readings come from faulty devices so I'm thinking I'm the one doing something especially stupid, or maybe a defect somewhere on the valve/tire but it's brand new, so I think I'm the one to blame. Any ideas where I've been an idiot?

I did open the nut on the presta valve prior to taking measurements.

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[–] j4k3 2 points 8 months ago* (last edited 8 months ago) (6 children)

Close the presta valve and see how high you can get the pressure reading, and if it maintains pressure or leaks immediately, even a small amount. A badly matched seal due to the valve stem could be a commonality. Is this a problem with both tires? What about other bikes you may have, can you test it on them?

[–] Natal 2 points 8 months ago (1 children)

Thank you for your answer! Appreciated. I only have that one bike, but it happens on both tires and, actually, one is tubed and one is tubeless. What I did is trying to get them to feel as close as possible in terms of firmness without actual data and then checked pressure. Both read the same PSI, give or take a couple points, which I attribute to the vagueness of pumping "to the touch".

I did what you asked and what happens is the following: I can get to 24.5 PSI before the pump resists very hard. I probably could force it a little more but I'm afraid to break something? The pressure stays there until I release the pump handle which was resisting, when I stop holding it, it goes back up somewhat and I lose a bit of PSI, but not all.

[–] j4k3 1 points 8 months ago (1 children)

What kind of pump are you using floor or hand?

[–] Natal 2 points 8 months ago (1 children)

It's a floor pump. This one: https://www.action.com/fr-fr/p/2561081/pompe-a-velo/ I also have a hand pump but I guess it's not particularly useful right now?

[–] j4k3 2 points 8 months ago (1 children)

This is my floor pump against a typical presta valve easily holding ~175psi. You should be able to get well over 100psi on any floor pump against a closed valve.

Take the bike/pump to a local bike shop to compare readings and pressures against a known good source or at least just take your pump(s) and verify against a known good pump.

[–] Natal 2 points 8 months ago (1 children)

There's no risk to using force? Maybe I just didn't push hard enough because I was scared to put too much pressure on the presta and bend it. They look weak.

[–] j4k3 1 points 8 months ago

No risk. Road can go well over 100 psi in road stuff all the time.

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